<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
       section{
            background: pink;
        }
        header{
            position: absolute;
        }
        /* 绝对定位可以让元素脱离文档 */
    </style>
</head>
<body>
    <header>头部</header>
    <section>toubu</section>
    
</body>
</html>